Acquiring the ability to communicate using natural language and symbolic gestures is a uniquely human capacity that underlies the exchange of information among people. There is as yet no consensus concerning how susceptible this process is to environmental and biological variation. The proposed Program Project focuses on this issue, exploring the extent and the limits of the language-learning process. To examine language growth in the face of environmental variation (Project I), 60 children, selected to represent the demographic range of the Chicago area, were observed between the ages of 14 and 58 mos. and will continue to be followed as they enter school and learn to read. Assessments will be made of child spontaneous speech, along with narrative and reading skills from 5 to 10 years. Using these data, growth curves will be constructed for each child to track language and reading development across time, and to examine children's linguistic and reading progress in the later years (5-10 yrs.) in relation to their developmental trajectory during the early years (14-58 mos.). To explore language growth in the face of biological variation (Project III), 40 children with unilateral brain injury who were observed from 14 to 58 mos. will be followed from 5 to 10 years with an eye toward determining whether environmental variation plays the same role in predicting their language and reading growth as it does in children who have not suffered brain injury. Along with traditional measures, two additional probes will be used. (1) Gesture will be examined in children from Projects l-lll to determine whether children who are delayed in speech relative to their peers use gesture to compensate for those delays (Project II). (2) The brain bases underlying linguistic and gestural competence will be assessed in children from Projects l-lll using fMRI techniques (Project IV). Three cores will provide broad support to the projects: the Administrative Core A, the Data Collection and Transcription Core B, and the Statistical Core C. The proposed work builds on five years of longitudinal data in a diverse sample, and thus offers a unique opportunity to explore the impact that early language learning has on the oral and written skills that children develop once schooling has begun. The data have the potential to shed light on the factors that contribute to the gap between children from high vs. low socioeconomic groups on the first day of school, and may even point to ways of shrinking that gap.